This invention relates to apparatus and techniques for the direct measurement of the size distribution of particles in a field of particles. More particularly, this invention relates to measurements of size parameters of mineral particles in mineral processing or quarry plants in which size distribution information is needed for quality or process control.
Data on size distribution is conventionally obtained by mechanical removal of a sample, passing the sample through screens of decreasing aperture, and weighing the material on each screen. Such an operation may be applied to moving material as for example on a conveyor belt, or static material in a stockpile. The present invention is particularly applicable to a field of physically moving particles. The mechanical sampling and sieving system has the disadvantage of being costly and not being substantially instantaneous, although the results obtained give a reproducible measurement of the weight of particles in each size range.
It has also been proposed to image a stationary surface by transmitted light, such as a microscope slide or a polished mineral surface, and scan the image by a raster scan with processing of the resultant signal. Such a system is complex and not suitable for macroscopic moving particle fields.